Given the title of Kanshu Sunadomari's book, I would be interested to see what he takes for granted about Japanese concepts of enlightenment. For example, have you come across the phrase "sokushin joubutsu"? It has been translated as "enlightenment in this very body", e.g., the one you've got. I think the phrase was first used by Kukai and underpins the culture of 'shugyou' that goes right back to his time. As you know, shugyou and keiko are used in traditional arts that are much older than aikido. So one might wonder whether people like Zeami and Sen no Rikyuu thought the same way about enlightenment through training in their respective arts.

So, when someone comes along and talks about enlightenment through aikido, people like myself want to know how much of this tradition he is taking for granted. Which is why in almost every case, whenever a Japanese scholar has produced a work that has been translated, I have tried to locate the Japanese original, so I can see what he actually wrote. And Omoto-kyou\the Sunadomaris were believers\is even more eclectic and also uses Christian sources. I have profited much from discussing aspects of this question with David Valadez in other threads.

Another interesting aspect of this discussion is that of levels. K Chiba has an interesting article on SHU-HA-RI and this can be interpreted in a linear fashion\proceeding from one to the other, or a layered fashion\moving up and down. However, (1) the concepts is used in arts that have been influenced by Buddhism and (2) SHU-HA-RI is only one way among many others of distinguishing levels of proficiency or awareness. I am not aware that M Ueshiba ever used the term.

I find the notion of levels or layers very useful in understanding budo and aikido and I suspect that this is because I have been brought up in the Graeco-Roman/Judaeo-Christian intellectual tradition.